I say, don't make assumptions unless you need them. Formatting an email address in an HTML document would work by wrapping it in the appropriate tag. (which implies html-quoting it correctly, but that is unrelated to email syntax).
Sending an email using an API would work by passing the email as a string to the API.
Looking up an email address from an address book using a pattern to match would be implemented with normal text search.
It doesn't matter if the email is "valid" or not. Don't overthink it.
I say, don't make assumptions unless you need them. Formatting an email address in an HTML document would work by wrapping it in the appropriate tag. (which implies html-quoting it correctly, but that is unrelated to email syntax).
Sending an email using an API would work by passing the email as a string to the API.
Looking up an email address from an address book using a pattern to match would be implemented with normal text search.
It doesn't matter if the email is "valid" or not. Don't overthink it.